1. Field of the Invention
This invention relates to surge or reaction-type trailer brakes, and more particularly to a trailer brake actuator with an improved slider arrangement that can withstand the rigors of movement over rough terrain when attached to a towing vehicle with a rotatable pintle.
2. Description of the Related Art
Surge brakes utilize the differential inertia between a towing vehicle and a towed trailer to mechanically displace fluid from a hydraulic brake master cylinder assembly actuating the brakes attached to the wheels of the trailer resulting in the deceleration of the trailer. One type of surge brake consists of a telescopic slider assembly affixed to the trailer and attached to a connector on the towing vehicle. When the towing vehicle brakes, the speed of the trailer exceeds the speed of the towing vehicle and the trailer attempts to "overrun" the towing vehicle. The momentum of the trailer causes the slider assembly to telescope inward thus causing the distance between the towing vehicle and the trailer to lessen. This movement results in the displacement of fluid in the brake master cylinder attached to the slider assembly, which actuates the trailer's brakes and slows the trailer. As the trailer slows and the slider assembly telescopes outward again, the movement results in the reduction of pressure in the braking system and ultimately effectuating complete disengagement of the trailer brakes.
Brake master cylinder assemblies that can be used on trailer surge brake actuators are well known in the prior art. Some brake master cylinders are rather rudimentary and cause the trailer to brake whenever the distance between the towing vehicle and the trailer is reduced to a predetermined distance. The disadvantage of this limitation is apparent when the towing vehicle is backing up. When the towing vehicle is backing up, the weight of the trailer may cause the slider assembly to telescope inward causing the actuation of the trailer brakes. This problem, however, is easily overcome by brake master cylinder assemblies configured to release the pressure in the brake system when the pressure reaches a predetermined amount or when the relative movement of the actuator parts exceeds a predetermined distance. A third type of brake master cylinder assembly combines the functions of the first two, but also allows braking in the reverse direction under some circumstances, such as for holding the trailer on a hill. All three of these brake master cylinders are well known in the prior art and each can be used with the present invention.
Also well known in the prior art are emergency breakaway features used on surge brakes which actuate the trailer brakes if the trailer becomes unexpectedly detached from the towing vehicle. Normally, the breakaway feature consists of a cable attached at one end to the towing vehicle and affixed at the other end of the cable to a pivotal lever attached to the mechanical linkage whose movement displaces the fluid in the brake master cylinder assembly. When the trailer coupling becomes detached from the towing vehicle and the distance between the towing vehicle and the trailer exceeds the length of the cable, the cable becomes taut and pulls the lever forward forcing the mechanical linkage to move into the brake master cylinder and displacing fluid from the brake master cylinder assembly resulting in the application of the trailer wheel brakes.
Although surge brakes are most often used on cargo or boat trailers, they are not limited to these applications. Surge brakes are equally applicable for use with other objects that are towed, such as motor homes or other motor vehicles.
The use of surge brakes on military trailers presents unique problems. Unlike commercial towing vehicles which have fixed coupling means attached to the towing vehicles, military vehicles have rotatable pintles. Rotatable pintles are a safety feature required by military specifications. The rotatable pintle can prevent the towing vehicle from "tipping over" if the trailer "tips over". Military trailers are prone to tipping over for a variety of reasons, such as use on uneven terrain at high speeds with frequent drastic maneuvers, improper cargo load distribution, and high ground clearance with a high center of gravity. The rotatable pintle rotates if the trailer tips over, thus, preventing the towing vehicle from tipping over also. If the pintle were not rotatable, the towing vehicle could also tip over under some circumstances. Military operational requirements also dictate that trailers withstand the rigors of extreme off-road use, far in excess of that placed upon commercial trailers.
The U.S. Army is currently developing and testing a suitable trailer for its High Mobility Multipurpose Wheeled Vehicle (HMMWV). Unlike other military trailers with hydraulic brakes, the new trailer must be capable of a gross vehicle weight (GVW) of up to 4200 pounds. Several commercially available surge brakes were tested for use on military trailers and proved unsatisfactory for military use. One common problem was that the telescoping slider assemblies and the mechanical linkages connected them to the brake master cylinder assemblies could not withstand the rigors of military cross country terrain use under such heavy loads.
Another major problem encountered was that the rotational movement of the pintle under normal military towing circumstances caused premature and uneven wear and failure of the surge brake assemblies. The pintle rotates to varying degrees when the trailer travels over uneven surfaces. The surge brakes tested had rather rudimentary anti-rotational devices attached to the surge brake to prevent premature wear of the slider assembly caused by the rotation of the slider assembly when the pintle rotated. 0n the surge brakes tested, the anti-rotational devices consisted of some type of metal L-shaped member with one end fixed to the slider and the other end inserted into a aperture that needed to be cut in the trailer frame directly below the slider assembly upon which the surge brake was affixed. The function of the L-shape member was to act like a positive lock whenever the pintle rotated and the L-shaped member moved slightly in the direction of rotation and came in contact with the side of the trailer frame surface on the periphery of the aperture. These rudimentary anti-rotational devices proved unsatisfactory. The end of the L-shaped member extending into the trailer frame wore prematurely because of the slight rotational movement of the L-shaped member, the abrasive nature of the operating environment (sand, dust, mud, etc.), and the extreme forces exerted upon it whenever the pintle on the towing vehicle rotated. Also, the slight movement of the L-shaped member permitted the slider to rotate slightly also, which caused premature and uneven wear on the slider assembly.
Therefore, there remains a need for a suitable surge brake actuator that overcomes the shortcomings identified above. Furthermore, the surge brake actuator for use on military trailers must not require more than minimal maintenance, must withstand the environmental rigors of military operations and must be easily mounted on a wide variety of trailers. The present invention satisfies these needs.